1. Field of the Invention
The present invention relates to a dual-polarization receiver, and more specifically to a dual-polarization receiver for receiving polarized wave signals whose directions are different from each other.
2. Related Art
In a communication system in the cross-polarization hot standby scheme according to Japanese Patent No. 3044633, either a horizontal polarized wave (H polarized wave) or a vertical polarized wave (V polarized wave) is used as a working system (active system) and the other is used as a backup system (standby system).
Therefore, in the communication system according to Japanese Patent No. 3044633, capacity which can be transmitted by using a single frequency is limited to capacity which can be transmitted by a single wireless communication device. As interference between cross polarized waves occurs even in a stationary state (both V and H dual polarized waves are in stationary states), an antenna with a high degree of identifying polarized waves or a polarized wave identification circuit need to be used. As C/N (Carrier to Noise) characteristics need to be large enough as the modulating scheme becomes multi-valued modulating scheme (for example, 128 QAM (Quadrature Amplitude Modulation) or the like), the configuration of the communication system according to Japanese Patent No. 3044633, in which interference between cross polarized waves looks like noise, has a problem in that it provides insufficient system gain, i.e., it does not assure usual link quality.
In order to reduce interference between cross polarized waves, a cross polarization interference canceller according to Japanese Patent Laid-Open No. 2004-172975 and 2002-158630, for example, may be used. The Japanese Patent Laid-Open No. 2004-172975 and 2002-158630, however, describes no remedy for malfunctions of a device.
Japanese Patent Laid-Open No. 6-232787 describes a remedy with 2+N configuration, in which two links are prepared as backup links. With 2+N configuration, however, frequency utilization efficiency is very low particularly when N is small.